Apparatus and method for molding simultaneously a plurality of semiconductor devices

ABSTRACT

Provided is a molding apparatus for molding simultaneously a plurality of semiconductor devices. The molding apparatus includes a mold, a plurality of plungers, and a plunger block. The mold is prepared to mold a plurality of semiconductor devices. The plurality of plungers are plunged into the mold to inject a molding compound that will encapsulate the semiconductor devices in the mold. The plurality of plungers are assembled with the plunge block to operate at the same time. Each of the plurality of plungers includes a load sensor and/or a contact sensor, so as to sense separately whether the plungers are improperly operating.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/298,033 filed on Nov. 15, 2002, the disclosure of which isincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of semiconductor devices, andmore particularly, to a molding apparatus and method by which, when amolding compound is injected into a mold to encapsulate simultaneously aplurality of semiconductor devices, abnormal operation of the moldingapparatus is detected.

2. Discussion of Related Art

In assembling semiconductor devices, a molding process encapsulatessemiconductor devices using a molding compound such as epoxy moldingcompound (hereinafter “EMC”) to mold the semiconductor devices intopackages. Preferably, prior to the molding process, a lead connectionprocess bonds the semiconductor devices to a lead frame. This moldingprocess is performed in a mass-production process to mold a large numberof semiconductor devices at the same time by an automatic moldingapparatus. Generally, the molding of a large number of semiconductordevices bonded to a lead frame is automatically repeated.

To mold a large number of semiconductor devices, a molding apparatusincludes a plunger block or a plunger unit having a plurality ofplungers. The plunger block generally includes about 10 plungers orless. The plungers are plunged into a mold to inject a molding compoundinto the mold. Here, the individual plungers move along with themovement of the plunger block so as to inject the molding compound intothe mold.

When the plungers ascend from below the mold into the mold to inject themolding compound into the mold, the plungers in the plunger block ascendnot separately but simultaneously with the ascent of the plunger block.With the application of such a plunger block type press, uniformpressure can be applied when molding a plurality of semiconductordevices at the same time.

However, when occasionally one or more of the plungers does not operateproperly, such as a plunger does not completely ascend even though theplunger block completely ascends, the molding compound will not becompletely injected into the mold, and thus the molding of asemiconductor device corresponding to the specific plunger may beincomplete. Further, if the ascent of the specific plunger isincomplete, excessive pressure may be applied on the specific plungerand further molding failures occur.

FIG. 1 is a cross-sectional view of a molding apparatus in whichsemiconductor devices are normally molded. FIG. 2 is a cross-sectionalview of a molding apparatus in which semiconductor devices areincompletely molded.

Referring to FIG. 1, as a plunger block (not shown) ascends, a plunger10 ascends into a plunger hole 27 formed into a mold 20. A moldingcompound 40, e.g., epoxy molding compound (EMC), which is placed on theplunger 10 and being melted into liquid, flows into molding cavities 25in the mold 20 due to pressure generated by the ascent of the plunger10. Here, the plunger 10 ascends with a predetermined pressure to injectthe molding compound 40. The molding cavities 25 are formed in apredetermined shape between a lower mold 21 and an upper mold 23 to formmolding products or packages 50 in a predetermined shape. The moldingcompound 40 is injected where a lead frame 30, to which semiconductordevices are bonded by a lead connection process, is installed in themolding cavities 25.

When the plunger 10 ascends completely, the liquid molding compound 40smoothly flows into the molding cavities 25 and completely fills themolding cavities 25. Thereafter, the molding compound 40 is fullysolidified to complete the molding products 50. Next, the plunger 10descends, the lower and upper molds 21 and 23 are separated from eachother, and the molding products 50 are taken away.

To normally complete the molding products 50, the plunger 10 mustsmoothly and completely ascend into and descend out of the mold 20 alongwith the plunger block. However, although the plunger block normallyascends, there is a case where one or more plunger in the plunger blockmay not normally ascend for several reasons.

Referring to FIG. 2, if a plunger 15 in a plunger block does notnormally ascend into a mold 20 even in a case where the plunger blocknormally ascends, the molding compound 40 cannot smoothly and fully flowinto molding cavities 25 in the mold 20 because the plunger 15 fails toapply full pressure to a molding compound 40. As a result, the moldingcavities 25 are not completely filled with the molding compound 40 andmolding products 55 are poorly completed. For example, semiconductordevices 31, which are placed on and electrically connected to a leadframe 30 by bonding wires 33, are incompletely encapsulated.

Such poor molding occurs mainly when the plunger 15 does not normallyascend due to abnormal friction with the sidewall of a plunger hole 27even though the plunger block normally ascends. Then, the plunger 15stops ascending, and thus incomplete injection or incomplete moldingoccurs.

The stopping or abnormal operation of the plunger block can be sensed ordetected when all of the plungers or a great majority of plungers in theplunger block simultaneously stop or abnormally operate. However, theabnormal operation of a small number of plungers in the plunger blockdoes not greatly affect the movement of the plunger block, and thus theabnormal operation may not be detected. In other words, in a plungerblock type press, since the movement of the plunger block causes theplungers to move together, there may be a certain specific plungeroperating abnormally even when the plunger block moves normally. Thus,it is difficult to individually sense the abnormal operations of certainspecific plungers.

Since semiconductor devices molding is continuously repeated in anautomatic molding apparatus for mass-producing semiconductor devices, ifthe abnormal operations of specific plungers cannot be detected, a largenumber of molding may be poor. In particular, as chip sizes ofsemiconductor devices become smaller, a plurality of molding cavities(25 of FIG. 1) are designed to correspond to one plunger (10 of FIG. 1)to improve productivity. Thus, if the abnormal operation of the plunger10 is not sensed quickly or in real-time, a large number of poorlymolded semiconductor devices may result. Also, if the abnormal operationof the specific plunger continues, not only will semiconductor devicesbe poorly molded, but the abnormal operation will also spread over themold to perhaps the entire automatic molding apparatus.

Therefore, a method or a molding apparatus is needed by which moldingproducts can be efficiently prevented from being poorly manufactured, byseparately detecting the abnormal operations of individual plungers inreal-time during a molding process.

SUMMARY OF THE INVENTION

The present invention is directed to an apparatus for molding aplurality of semiconductor devices at the same time. According to apreferred embodiment of the present invention, when a plurality ofplungers in a plunger block ascend into a mold with the ascent of theplunger block so as to apply pressure to a molding compound, abnormaloperations of certain specific plungers are separately sensed to preventthe semiconductor devices from being poorly molded repeatedly, therebyefficiently enhancing productivity of molding a large number ofsemiconductor devices.

According to a preferred embodiment of the present invention, there isprovided a molding apparatus for molding semiconductor devices that arewire-bonded to a lead frame. The molding apparatus includes a mold, aplurality of plungers, a plurality of sensors, and a plunger block. Themold is used to mold a plurality of semiconductor devices. The pluralityof plungers are plunged into the mold to inject a molding compound thatwill encapsulate the semiconductor devices in the mold. The plurality ofsensors are installed under the respective plungers to sense whether theplungers operate abnormally. The plurality of plungers are assembledwith the plunger block to operate at the same time.

Here, the plunger block is positioned under the mold so that theplurality of plungers move from below the mold into the mold, and isoperated to move up and down so that the plungers move up and down.

According to another embodiment, a molding apparatus may include a mold,a plurality of plungers, a plunger block, and a plurality of loadsensors. The mold is used to mold a plurality of semiconductor devices.The plurality of plungers are plunged into the mold to inject a moldingcompound that will encapsulate the semiconductor devices in the mold.The plurality of plungers are assembled with the plunger block tooperate at the same time. The plurality of load sensors are installed atrespective plungers to sense pressures that are generated when therespective plungers operate.

The molding apparatus may further include plungers each of which has aplunger protrusion, a limit bar which limits movement of the plungers toa predetermined extent that prevents the plungers from deviating fromthe plunger block, and a plurality of contact sensors which sensewhether each plunger protrusion of the plungers contacts the limit baralong with normal operation of the plungers.

Here, the plunger block is positioned under the mold so that theplurality of plungers move from below the mold into the mold, and movesup and down so that the plungers ascend and descend. The limit barallows the plungers to ascend into the mold as far as they can go so asto inject the molding compound into the mold, contacts plungerprotrusions of the plungers when the plunger block starts to descend,and causes the plungers to descend along with the continuous descent ofthe plunger block.

Here, the contact sensors may be installed at contact positions betweenthe limit bar and the plunger protrusions of the plungers to contact theplunger protrusions of the plungers when the plungers start normallydescending. If one of the contact sensors does not contact a plungerprotrusion of a corresponding plunger when the plungers start normallydescending, the contact sensor senses that the corresponding plunger isoperating abnormally.

The limit bar may contact the plunger protrusions of the plungers whilethe plunger block waits to ascend so that the contact sensors contactthe plunger protrusions of the plunger. Also, the limit bar is separatedfrom the plunger protrusions of the plungers when the plungers areascending along with the ascension of the plunger block so that thecontact sensors separate from the plunger protrusions of the plungers.

According to embodiments of the present invention, when a plurality ofplungers in a plunger block are moved into a mold by moving the plungerblock to apply pressure to a molding compound, the abnormal operation ofa specific plunger can be detected by separately sensing the abnormaloperations of the plungers. Thus, the continuous repetition of poormolding due to an abnormal operation of a specific plunger can beprevented during a molding process. As a result, poor molding productscan be efficiently prevented from being mass-produced.

These and other aspects and features of the present invention will bedescribed or become apparent from the following detailed description ofpreferred embodiments, which is to be read in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a conventional molding apparatus bywhich semiconductor devices are molded;

FIG. 2 is a cross-sectional view of a conventional molding apparatuswhen semiconductor devices are improperly molded;

FIG. 3 is a cross-sectional view of a mold and a plunger used in amolding apparatus according to an embodiment of the present invention;

FIG. 4 is a perspective view of a lower mold used in a molding apparatusaccording to an embodiment of the present invention;

FIG. 5 is a cross-sectional view of a molding apparatus according to anembodiment of the present invention;

FIG. 6 is a cross-sectional view of a molding apparatus according to anembodiment of the present invention;

FIG. 7 is a cross-sectional view of a molding apparatus according to anembodiment of the present invention; and

FIGS. 8 through 11 are cross-sectional views for illustrating a processof detecting an abnormal operation of a plunger in a molding apparatusaccording to preferred embodiments of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention, hereinafter, will bedescribed in detail with reference to the attached drawings. In thedrawings, the thicknesses of layers or regions are exaggerated forclarity. Like reference numerals in the drawings denote the samemembers.

According to an embodiment of the present invention, there is providedan apparatus for molding semiconductor devices, which is configured toinject a molding compound into a mold based on pressure generated byindividual plungers ascending along with the ascent of a plunger blockincluding the plurality of plungers. Preferably, the molding apparatusmay be an automatic molding apparatus in which a molding process isautomatically repeated to mold a large number of semiconductor devices.

According to another embodiment of the present invention, there isprovided a molding apparatus, in which a plurality of plungers ascendfrom below a mold into the mold and inject a molding compound toencapsulate the semiconductor devices in the mold. It is to be noted,however, that, the plungers may move in other directions depending onthe structure of the molding apparatus.

Detecting units according to preferred embodiments of the presentinvention are provided for sensing the abnormal operation of a specificplunger in a plunger block when the plunger block ascends. The detectingunits can detect the abnormal operation of the specific plunger inreal-time to prevent a large number of semiconductor devices from beingincompletely molded.

FIG. 3 is a cross-sectional view for explaining operations of a mold 200and a plunger 110 used in a molding apparatus according to an embodimentof the present invention. FIG. 4 is a perspective view for explainingthe mold used in the molding apparatus according to the embodiment ofthe present invention.

Referring to FIGS. 3 and 4, the mold 200, which is used in a process ofpackaging, in particular, molding semiconductor devices, includes alower mold 210 and an upper mold 230. The lower mold 210 faces the uppermold 230 to form molding cavities 250. A lead frame 300, which supportswire-bonded semiconductor devices, is installed in the molding cavities250.

Since a plurality, for example, several tens, of molding cavities 250are included in one mold 200, a lead frame strip, to which a pluralityof semiconductor devices are wire-bonded, is positioned between thelower and upper molds 210 and 230. Here, the semiconductor devices arearranged to position in the molding cavities 250 of the mold 200.

A plunger 110 ascends and is plunged into a plunger hole 270 to applypressure to a molding compound 400 and to inject the molding compound400, e.g., EMC, into the molding cavities 250 of the mold. A pluralityof plunger holes 270 are configured in the mold 200 to allow a pluralityof plungers 110 to move back and forth in the mold 200 along with themovement of a plunger block. The plunger holes 270 are formed in thelower mold 210 as shown in FIG. 4 to allow the plungers 110 to ascendand perform the injection process. As shown in FIG. 4, a plurality ofmolding cavities 250 may be connected to one plunger hole 270 tomass-produce semiconductor device packages.

The molding apparatus is automated to mass-produce molding products. Theautomatic molding apparatus repeats the processes of mounting a leadframe strip in a mold, injecting an EMC into the mold and hardening theEMC. The structures of the mold 200 and the plunger 110 shown in FIGS. 3and 4 may be applied to an automatic molding apparatus. The automaticmolding apparatus also includes an in-magazine part (not shown) in whichsemi-manufactured lead frames are stacked to automatically provide thesemi-manufactured lead frames to the mold 200. The automatic moldingapparatus further includes a tablet part which supplies a tabletcompound to molding facilities. The automatic molding apparatus alsoincludes a loader part which supplies the stacked lead frames or themolding compound, i.e., an EMC tablet, to the mold. The automaticmolding apparatus further includes an unloader part which unloadspackaged molding products from the mold and a stack part which stacksthe packaged molding products.

FIG. 5 is a cross-sectional view for explaining structure of a moldingapparatus according to one embodiment of the present invention.Referring to FIG. 5, as described with reference to FIGS. 3 and 4, theplunger block 100 includes a plurality of plungers 110 which arearranged to plunge into a plurality of plunger holes 270 in a mold 200,respectively. In FIG. 5, one plunger block 100 includes four plungers110, but a certain plunger block may include more than four plungers110.

The plungers 110 are supported by a plunger block housing 101. Buffersupports 130 are placed beneath the plungers 110, respectively, so thatthe plungers 110 are supported by the bottom surface of the plungerblock housing 101. Here, the plungers 110 are just placed on the buffersupports 130. Also, some other interconnecting parts may be incorporatedbetween the plungers 110 and the buffer supports 130. The buffersupports 130 uniformly distribute and maintain pressure generated whenthe plungers 110 ascend along with the movement of the plunger block100. Thus, the buffer supports 130 may include elastic members such ascompression springs.

Separators 170 separate the plungers 110 from one another in the plungerblock housing 101. A lower limit part 175 may be assembled at the upperend of a separator 170 and over the buffer supports 130 to limit theheights of the buffer supports 130 so that the plungers 110 aresupported by the buffer supports 130 in a predetermined startingposition.

The plunger block housing 101 includes the buffer supports 130. A limitbar 105 is joined with the upper position of the plunger block housing101. Each of the plungers 110 includes plunger protrusion 113 forlimiting travel of corresponding plunger 110 at the limit bar 105. Theplunger protrusions 113 and the limit bar 105 also prevent theindividual plungers 110 from deviating from the plunger block housing101. The limit bar 105 serves to transfer a force from the plunger block100 to the plungers 110 when the plunger block 100 descends after theplungers 110 ascend.

Load sensors 500 are placed between the buffer supports 130 and thebottom surface of the plunger block housing 101. A load sensor 500 isinstalled under each of the plungers 110 to support the buffer supports130. Each of the load sensors 500 detects loads applied to acorresponding plunger 110, senses load pressures generated during theoperations of the corresponding plunger 110, and transmits the sensedpressures to a pressure detector 550.

The pressure detector 550 transmits the numerical values of thepressures to a determining unit 700. The determining unit 700 determinesthe numerical values of the pressures applied to the plungers 110 todetermine whether the plungers 110 operate normally. For example,assuming that the numerical values of the pressures detected by the loadsensors of the plungers 110 are P.sub.1, P.sub.2, P.sub.3, and P.sub.4,and a normal pressure applied when the plungers 110 operate normally isP, the determining unit 700 compares the numerical values P.sub.1,P.sub.2, P.sub.3, and P.sub.4 with the pressure P to determine whetherthere is an abnormal pressure. In one embodiment, the determining unit700 determines how much the numerical values obtained from the plungersdeviate from the normal pressure P. The determining unit 700 warns auser about any abnormal pressures and informs the user as to whichplunger is generating an abnormal pressure.

As described above, by installing a load sensor 500 under each of theplungers 110, a specific plunger that generates an abnormal pressureduring the molding process can be sensed in real-time. As a result, whena specific plunger 110 operating abnormally is detected, the moldingprocess can be stopped and poorly molded products are not mass produced.

FIG. 6 is a cross-sectional view of a molding apparatus according toanother embodiment of the present invention. Referring to FIG. 6, atouch sensor 600 is installed between each of plunger protrusions 113and a limit bar 105. Touch sensors 600 sense whether the plungerprotrusions 113 contact or touch touch sensors 600, respectively. Forexample, each of the touch sensors 600 may include electrical circuits(not shown), which are constituted to apply currents to the circuitsonly when the plunger protrusions 113 contact or touch the touch sensors600. Signals of the touch sensors 600 are transmitted to a contactdetector 650. The determining unit 700 analyses the signals, determineswhether the plungers 110 are operating abnormally, and informs a user asto whether the respective plungers 110 are operating normally orabnormally.

Assuming that the plungers 110 are operating normally during a moldingprocess, the plungers 110 ascend, and after the molding process iscompleted, the plungers 110 are positioned in an initial descendingposition. However, if the plungers 110 are operating abnormally, theplungers 110 fail to position in the initial descending position eventhough the molding process is completed. In more detail, a moldingcompound 400 is injected after the plunger block 100 completely ascends,and the plunger block 100 descends after the molding process iscompleted in the normal process.

At the initial stage of descent of the plunger block 100, the plungerblock starts moving down while the plungers 110 maintain their positionswhen the molidng process is just completed. In other words, the plungers110 maintain their positions at the maximum ascent height. Thus, at theearly stage of the descension of the plunger block and the plungers, theplunger block 100 first descends. Since the plunger block 100 descendsand the plungers 110 maintain their positions, the plunger protrusions113 of the plungers 110 contact the limit bar 105 as the plunger blockdescends in case the plungers 110 operate normally. In this case, theplunger protrusions 113 contact the touch sensors 600.

A specific one of the plungers 110 corresponding to one of the plungerprotrusions 113 that does not contact the one of the touch sensors 600at the early stage of descension may be regarded as operating abnormallyduring the molding process. Since the specific one of the plungers 110,which abnormally ascended, is lower than the other plungers 110, theplunger protrusion 113 of the specific plunger 110 does not contact acorresponding contact sensor 600 while each of the other plungerprotrusions 113 normally contacts each of corresponding touch sensors600, respectively. Since the touch sensors 600 sense whether the plungerprotrusions 113 contact the touch sensors 600, the touch sensors 600 cansense whether the respective plungers 100 operate abnormally.

FIG. 7 is a cross-sectional view for explaining a molding apparatusaccording to another embodiment of the present invention. Referring toFIG. 7, it can be precisely sensed whether plungers 110 operateabnormally by combining methods described above with reference to FIGS.5 and 6.

Preferably, touch sensors 600 are installed between plunger protrusions113 of the plungers 110 and a limit bar 105. The touch sensors 600 sensewhether the plunger protrusions 113 contact the touch sensors 600 andtransmit contact or non-contact signals to a contact detector 650. Thecontact detector 650 transmits the contact or non-contact signals to adetermining unit 700.

Load sensors 500 are installed under the plungers 110 between buffersupports 130 and the bottom 102 of a plunger block housing 101,respectively. The load sensors 500 detect loads or pressures that areapplied to the respective plungers 110 corresponding to the load sensors500, sense load pressures generated during the operations of theplungers 110, and transmit signals of the load pressures to a pressuredetector 550. The pressure detector 550 detects pressure values from theload sensors 500 and transmits the pressure values to the determiningunit 700.

The determining unit 700 determines whether the plungers 110 operatenormally based on the pressure values and the contact or non-contactsignals. In case the abnormal operation of a specific one of theplungers 110 is sensed due to an abnormal pressure, the determining unit700 warns a user of the abnormal operation, and provides the user withinformation about the specific plunger 110.

By detecting whether the specific plunger 110 operates abnormallyaccording to the methods described above, the reliability of sensingwhether the specific plunger 110 operates abnormally can be effectivelyincreased.

FIGS. 8 through 11 are cross-sectional views for explaining a process ofdetecting the abnormal operation of a specific plunger of the moldingapparatus according to preferred embodiments of the present invention.

FIG. 8 is a cross-sectional view illustrating positions of plungers inthe early molding stage. FIG. 9 is a cross-sectional view illustratingpositions of plungers while the plungers ascending in a molding process.FIG. 10 is a cross-sectional view illustrating positions of plungerswhen the plungers complete ascending in the molding process. FIG. 11 isa cross-sectional view illustrating positions of plungers when theplungers start descending after the molding process is completed.

Referring to FIG. 8, a lead frame strip (not shown) onto whichsemiconductor devices are wire-bonded is installed between an upper mold230 and a lower mold 210 to arrange the semiconductor devices in moldingcavities (250 of FIG. 3). Plungers 110 are plunged into respectiveplunger holes 270 in the mold 230, and a molding compound 400, e.g.,EMC, is melted into liquid on the ends of the plungers 110 and isinjected into the mold 230. The processes of employing the lead framestrip and EMC are automatically performed in an automatic moldingapparatus.

In the initial stage of the molding process, the plungers 110 are in theinitial positions for molding. The plunger protrusions 113 of theplungers 110 contact the bottom of the limit bar 105 of the plungerblock 100. Where touch sensors 600 are installed as in FIG. 6, theplunger protrusions 113 contact the touch sensors 600, and the touchsensors 600 signal a contact of the plunger protrusions 113 and thetouch sensors 600 to a contact detector 650 and a determining unit 700.In the early molding stage, the plungers 110 in the plunger block 100,in a normal case, are all positioned to contact the touch sensors 600.

Referring to FIG. 9, when the molding compound 400, e.g., EMC, is fullychanged to liquid for injection into the mold 200, plungers 110 in theplunger block 100 ascend along with the ascension of the plunger block100. Plunger protrusions 113 are separated from the bottom of the limitbar 105 due to pressures generated when the plungers 110 ascend. Iftouch sensors 600 are installed (on the limit bar 105), the plungerprotrusions 113 separate from the touch sensors 600.

Preferably, when the plunger block 100 ascends, i.e., the plungers 110ascend, positions of buffer supports 130 and the ascension pressure ofthe plunger block 100 are controlled to position the plunger protrusions113 between the limit bar 105 and a lower limiting part 175.

It is normal for the plungers 110 in the plunger block 100 to movesmoothly up and down along with the movement of the plunger block 100.However, some specific plungers may operate abnormally due to reasonssuch as an increase in abnormal friction forces between the plungers 110and plunger holes 270.

Referring to FIG. 10, when plungers 110 ascend to a predeterminedmaximum height with the completion of the ascent of the plunger block100, the injection of EMC into a mold 200 is completely performed. Here,it is normal for the plungers 110 to ascend to their maximum heights.However, a specific plunger 110′ operates abnormally due to a harmfulcause such as a rise in abnormal friction force. In other words, thespecific plunger 110′ stops ascending in the middle of its ascent andthus does not reach its predetermined maximum height.

However, since the abnormal operations of a small minority of plungersdo not greatly affect the operation of the plunger block 100, theplunger block 100 continues to ascend. Thus, the other normal plungers110 continue to ascend to complete the injection of the EMC. Since thespecific plunger 110′ does not ascend, the injection of the related EMCis not completed.

Since the specific plunger 110′ stops ascending, the specific plunger110′ is lower than the other normal plungers 110. Since the specificplunger 110′ stops ascending while the plunger block 100 continuesascending, a high abnormal pressure is generated on the specific plunger110′, compared to pressures on the other normal plungers 110. A loadsensor 500′, which is positioned under the specific plunger 110′, sensesthe abnormal pressure of the specific plunger 110′ and transmits it to apressure detector 550. A determining unit 700 compares the abnormalpressure signal detected from the specific plunger 110′ with normalpressure signals detected from the other normal plungers 100 todetermine whether the specific plunger 110′ operates abnormally andsignals the abnormal operation of the specific plunger 110′ for theuser.

Using an alarm system, it can be sensed in real-time whether thespecific plunger 110′ operates abnormally so as to quickly cope with theabnormal operation. Therefore, poorly molded products (or packages) dueto repeated abnormal operation of the specific plunger 110′ during anautomatically repeated molding process can be prevented from beingmass-produced.

Referring to FIG. 11, the plunger block 100 starts descending after theinjection of a molding compound 400 and the completion of the molding.Here, the descending operation of the plunger block 100 makes touchsensors 600 contact with plunger protrusions 113 of normal plungers 110.Thus, the touch sensors 600 generate normal contact signals and transmitthe normal contact signals to the contact detector 650. The determiningunit 700 informs a user that the plungers 110 are operating normally,based on the normal contact signals.

Thereafter, as the plunger block 100 continues descending, the plungers110 operate normally, continue to descend, and return to the initialposition. The molding process is automatically repeated in an automaticmolding apparatus.

However, since the specific plunger 110′, which abnormally operatesduring its ascent, stops ascending, the specific plunger 110′ is lowerthan the other normal plungers 110. Thus, a plunger protrusion 113″ ofthe specific plunger 110′ fails to make contact with a contact sensor600′ while the plunger protrusions 113 of the other normal plungers 110make contact with the respective touch sensors 600, and generate contactsignals. As a result, since the contact sensor 600′ cannot provide acontact signal to the contact detector 650, the determining unit 700warns a user of the abnormal operation.

As proposed in FIG. 7, with a combination of these two methods ofsensing abnormal operations, an abnormal operation of a specific plunger110′ can be precisely sensed. Thus, the reliability of warning a userabout the abnormal operation is increased.

When normal descending is performed, a plunger block 100 continues todescend. Thus, plungers 110 also continue to descend and return to theirpositions in the early molding stage as shown in FIG. 8. The moldingprocess is automatically repeated in an automatic molding apparatus. Ifthe abnormal operation of the specific plunger 110′ is not sensed, poormolding is repeated due to the abnormal operation of the specificplunger 110′. However, as described in the present invention, since theabnormal operation of the specific plunger 110′ can be efficiently andreliably sensed during the molding process, poorly molded products dueto the repetition of poor molding can be prevented from beingmass-produced.

According to preferred embodiments of the present invention, when alarge number of semiconductor devices are packaged using a plunger blockhaving a plurality of plungers in a molding apparatus, the abnormaloperation of a specific plunger can be efficiently sensed when theplunger block is operating. Thus, when the molding process isautomatically repeated, poorly molded products or packages due to theabnormal operation of the specific plunger can be prevented.

Although the invention has been described with reference to particularembodiments, the embodiments of the present invention can be modifiedinto various other forms, and the scope of the present invention mustnot be interpreted as being restricted to the embodiments. It will beapparent to one of ordinary skill in the art that modifications of thedescribed embodiments may be made without departing from the spirit andscope of the invention.

1. A method for detecting abnormal operation in simultaneously molding aplurality of semiconductor devices, the method comprising the steps of:sensing pressures that are generated while a plurality of plungersascend and descend; limiting movement of the plungers to a predeterminedextent that prevents the plungers from deviating from a plunger block;injecting a molding compound to encapsulate the plurality of thesemiconductor devices in a mold using the plurality of plungers;comparing values of the pressures generated while the plurality ofplungers ascend and descend with a value of normal pressure applied whenthe plungers operate properly; and determining whether the plungersoperate improperly.
 2. A method for detecting abnormal operation insimultaneously molding a plurality of semiconductor devices, the methodcomprising the steps of: limiting movement of the plungers to apredetermined extent that prevents the plungers from deviating from aplunger block which has a limit bar; injecting a molding compound toencapsulate the plurality of the semiconductor devices in a mold usingthe plurality of plungers, each of the plungers having plungerprotrusions; sensing whether the plunger protrusions of the plurality ofplungers contact the limit bar during operation of the plungers;determining whether the plungers operate improperly, wherein if aplunger protrusion of a corresponding plunger is not in contact with thelimit bar when the plungers start descending, the corresponding plungeris determined as operating improperly.